The present invention is directed to functionally gradient polycrystalline cubic boron nitride materials, to tools incorporating such materials.
Polycrystalline cubic boron nitride has been used extensively as a cutting surface in various cutting tools. Polycrystalline cubic boron nitride (PCBN) is formed by placing cubic boron nitride grains, a second phase and a binder phase within a refractory metal enclosure and then sintering the enclosure with its contents at high pressure and high temperature (HPHT) conditions for forming the PCBN. PCBN materials may be tailored to either provide better strength, better toughness, better chemical wear, or better thermal stability. However, as the magnitude of any of these properties is increased, the magnitudes of the remaining properties may be decreased. To overcome this problem, PCBN material layers which have been used in cutting tools, have in many instances, been coated with a thin film, such as Al2O3 or TiN, which is more chemically and thermally stable than PCBN during severe cutting conditions. These films reduce the initial chemical wear and the mechanical wear of the PCBN. The problem however with these coatings is that they tend to debond, flake off or wear off from the PCBN layer. This is especially prevalent during machining with a coated PCBN layer.